Gas-measuring devices, especially portable gas-measuring devices, are used to monitor the gas concentration of at least one gaseous substance in a predetermined operating area, e.g., an industrial plant, such as a refinery. The gaseous substances may be, e.g., carbon monoxide, hydrogen sulfide, oxygen or other toxic gaseous substances. These gas-measuring devices have for this one or more sensors in order to measure the gas concentration of the gaseous substance in question in the ppm range. Such gas-measuring devices usually have two limit values, which trigger an alarm. These are a low limit value, where a pre-alarm (also called A1) is triggered when this is exceeded, and a high limit value, where a master alarm (also called A2) is triggered when this is exceeded. The gas-measuring device generates an acoustic and/or optical alarm in order to warn the user of the gas-measuring devices in response to the exceeding of a limit value, for example, a workplace limit value (WLV) or a lower explosion limit (LEL), which sets the maximum allowable concentration of a gaseous substance. To guarantee reliable operation of the gas-measuring devices, it is necessary for the gas-measuring devices to be checked regularly. For example, so-called bump tests are carried out for this at relatively short intervals and calibrations at relatively long intervals compared to the former. These bump tests and calibrations are carried out with so-called docking stations, which admit for this an inert gas, e.g., nitrogen, or fresh air, and a test gas containing the gaseous substance to be detected to the sensor of a gas-measuring device. However, it is desirable to obtain more information on the safety situation in a predetermined operating area.